This invention relates to methods and apparatus for generating electrical, thermal or mechanical energy from the oxidation of aluminum or its alloys, especially from aluminum waste and other inexpensive aluminum products.
In my copending applications and prior patents, I have disclosed apparatus and methods for withdrawing electrical energy, heat, and an aluminum hydroxide reaction product from the electrochemical oxidation of aluminum, preferably in aqueous alkaline electrolytes. The present invention deals with apparatus and methods for generating mechanical or electrical energy from the oxidation of aluminum without necessarily resorting to aqueous alkaline systems or even to electrochemical energy conversion.
Electrochemical power sources usually necessitate a number of series-connected cells to provide the required voltage. Moreover, the electrochemical aluminum-consuming systems disclosed thus far usually necessitate electrolyte circulation through these cells, which in turn introduces current leakage problems. The complexity of such series-connected systems increases their cost and may affect their reliability.
It is therefore an object of my invention to provide aluminum-consuming power sources which are simpler in design and operation, and cheaper to manufacture and maintain.
Closed-cycle thermal energy conversion systems have been developed and perfected during the last century, and especially during the last few decades to the point of providing energy conversion efficiencies of up to about 40% and of being fairly compact and relatively simple in design. With the enthalpy of oxidation of aluminum being equivalent to nearly 3 electron-volts, a thermal aluminum-consuming engine operating at an efficiency of between 30% and 40% becomes equivalent to an electrochemical power system yielding between 0.9 volt and 1.2 volt/cell at 100% faradaic efficiency.
It is therefore a further object of my invention to provide a thermal engine deriving its heat from the enthalpy of oxidation of aluminum.
Beside being simpler and more compact than electrochemical power systems, thermal engines are also capable of operating at higher peak power densities. In addition, the aluminum hydroxide reaction product in electrochemical systems has a high water content and is rather voluminous to start with, and said water content can only be reduced through special processing, requiring auxiliarys equipment, whereas the aluminum oxide reaction product of a thermal engine must be dry to start with due to the elevated combustion temperature required for a high energy conversion efficiency.
It is therefore still another object of my invention to provide an aluminum-consuming power source having high overall energy storage and power densities.
In alternative embodiments of my invention, the energy conversion means is still electrochemical rather than thermal. However, it differs from previously disclosed aluminum-consuming electrochemical cells in using a non-caustic or only mildly caustic electrolyte.
Non-alkaline primary aluminum batteries are known in the art. However, such batteries have utilized aluminum alloys of special composition.
It is yet another object of my invention to provide non-alkaline aluminum consuming electrochemical cells which do not necessitate the use of special alloys
It is still another object of my invention to provide aluminum-consuming power sources which can utilize disposable aluminum cans or other inexpensive forms of aluminum as their primary fuel.